An example attack launched against voice over Internet protocol (VoIP) networks is a so called Denial-of-Service (DoS) attack, which is instigated by, for example, launching large numbers of call setup requests into a VoIP network. For example, in a session initiation protocol (SIP) based network, a large number of SIP INVITE messages may be used to cause high utilization in SIP protocol processors. When processor utilization becomes sufficiently high, initiated communication sessions (both those associated with the attack and benign calls) become effectively blocked.